Poly(1,4-butylene terephthalate) resins are well know and have been widely employed for the production of thermoplastic molded articles. Also, reinforced compositions of poly(1,4-butylene terephthalate) have been commercially available for a number of years. Unfilled poly(1,4-butylene terephthalate) has good processability, strength and toughness. Other key properties include low water absorption resulting in good dimensional stability, low static and dynamic coefficients of friction, good chemical and abrasion resistance, and good electrical properties. However, the unfilled poly(1,4-butylene terephthalate) has a relatively low heat deflection temperature which limits its use. Also, unfilled poly(1,4-butylene terephthalate) has a tendency to shrink to a great extent after being molded.
Reinforced poly(1,4-butylene terephthalate) and, particularly, glass reinforced poly(1,4-butylene terephthalate) has additionally increased tensile strength over the unfilled poly(1,4-butylene terephthalate). However, when molded, reinforced, particularly glass reinforced poly(1,4-butylene terephthalate) has a tendency to become distorted or warped.
U.S. Pat. No. 4,125,571 discloses a thermoplastic composition comprising a combination of poly (1,4-butylene terephthalate) and a polyester resin derived from cyclohexanedimethanol and a hexacarbocyclic dicarboxylic acid such as terephthalic acid. It was found that the shrinkage of poly (1,4-butylene terephthalate) resin was reduced while increasing the heat deflection temperature. Reinforced polybutylene terephthalate molding compositions had increased resistance to warpage or distortion upon removal from the mold upon adding the polyester resin derived from cyclohexanedimethanol. The patent broadly states that cyclohexanedimethanol and minor amounts of other bifunctional alcohols can be condensed with the dicarboxylic acid. Examples of such bifunctional glycols include ethylene glycol, butylene glycol, etc. However, the patent does not describe any minimum or maximum for the minor amounts of other bifunctional glycols to be included in the polyester resin. The examples in this U.S. patent are directed to a poly(1,4-cyclohexanedimethanol terephthalate-co-isodialate) resin which is sold under the trade name of KODAR A150, from Eastman Chemical Products.
U.S. Pat. No. 4,225,688 discloses a copolyester composition which exhibits good bonding characteristics to polyvinylchloride plastics, consisting essentially of: from 80-95% by weight of a rigid poly(ethylene cyclohexanedimethylene terephthalate) such as exemplified by the commercial product KODAR PETG 6763; and 5-20% by weight of a flexible copolymer containing alternating blocks of poly(butylene terephthalate) and poly (1,4 butylene oxide) as exemplified by Hytrel a commercial product from the E.I. Dupont de Nemours and Company.
U.S. Pat. No. 4,287,325 discloses a polyester blend comprising a copolyester formed from terephthalic acid, isophthalic acid and bisphenol A and a polyester derived from terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol.
U.S. Pat. No. 4,582,876 discloses a molding composition having high impact which comprises a blend of a copolyester formed from terephthalic acid, 1,4-cyclohexanedimethanol and ethylene glycol and a rubber-modified styrene-maleic anhydride copolymer.